The present invention relates to conjugates, compositions, methods of synthesis, and applications thereof. The discussion is provided only for understanding of the invention that follows. This summary is not an admission that any of the work described below is prior art to the claimed invention.
The cellular delivery of various therapeutic compounds, such as antiviral and chemotherapeutic agents, is usually compromised by two limitations. First the selectivity of therapeutic agents is often low, resulting in high toxicity to normal tissues. Secondly, the trafficking of many compounds into living cells is highly restricted by the complex membrane systems of the cell. Specific transporters allow the selective entry of nutrients or regulatory molecules, while excluding most exogenous molecules such as nucleic acids and proteins. Various strategies can be used to improve transport of compounds into cells, including the use of lipid carriers and various conjugate systems. Conjugates are often selected based on the ability of certain molecules to be selectively transported into specific cells, for example via receptor mediated endocytosis. By attaching a compound of interest to molecules that are actively transported across the cellular membranes, the effective transfer of that compound into cells or specific cellular organelles can be realized. Alternately, molecules that are able to penetrate cellular membranes without active transport mechanisms, for example, various lipophilic molecules, can be used to deliver compounds of interest. Examples of molecules that can be utilized as conjugates include but are not limited to peptides, hormones, fatty acids, vitamins, flavonoids, sugars, reporter molecules, reporter enzymes, chelators, porphyrins, intercalcators, and other molecules that are capable of penetrating cellular membranes, either by active transport or passive transport.
The delivery of compounds to specific cell types, for example, cancer cells or cells specific to particular tissues and organs, can be accomplished by utilizing receptors associated with specific cell types. Particular receptors are overexpressed in certain cancerous cells, including the high affinity folic acid receptor. For example, the high affinity folate receptor is a tumor marker that is overexpressed in a variety of neoplastic tissues, including breast, ovarian, cervical, colorectal, renal, and nasoparyngeal tumors, but is expressed to a very limited extent in normal tissues. The use of folic acid based conjugates to transport exogenous compounds across cell membranes can provide a targeted delivery approach to the treatment and diagnosis of disease and can provide a reduction in the required dose of therapeutic compounds. Furthermore, therapeutic bioavialability, pharmacodynamics, and pharmacokinetic parameters can be modulated through the use of bioconjugates, including folate bioconjugates. Godwin et al., 1972, J Biol. Chem., 247, 2266-2271, report the synthesis of biologically active pteroyloligo-L-glutamates. Habus et al., 1998, Bioconjugate Chem., 9, 283-291, describe a method for the solid phase synthesis of certain oligonucleotide-folate conjugates. Cook, U.S. Pat. No. 6,721,208, describes certain oligonucleotides modified with specific conjugate groups. The use of biotin and folate conjugates to enhance transmembrane transport of exogenous molecules, including specific oligonucleotides has been reported by Low et al., U.S. Pat. Nos. 5,416,016, 5,108,921, and International PCT publication No. WO 90/12096. Manoharan et al., International PCT publication No. WO 99/66063 describe certain folate conjugates, including specific nucleic acid folate conjugates with a phosphoramidite moiety attached to the nucleic acid component of the conjugate, and methods for the synthesis of these folate conjugates. Nomura et al., 2000, J. Org. Chem., 65, 5016-5021, describe the synthesis of an intermediate, alpha-[2-(trimethylsilyl)ethoxycarbonl]folic acid, useful in the synthesis of ceratin types of folate-nucleoside conjugates. Guzaev et al., U.S. Pat. No. 6,335,434, describes the synthesis of certain folate oligonucleotide conjugates.
The delivery of compounds to other cell types can be accomplished by utilizing receptors associated with a certain type of cell, such as hepatocytes. For example, drug delivery systems utilizing receptor-mediated endocytosis have been employed to achieve drug targeting as well as drug-uptake enhancement. The asialoglycoprotein receptor (ASGPr) (see for example Wu and Wu, 1987, J. Biol. Chem. 262, 4429-4432) is unique to hepatocytes and binds branched galactose-terminal glycoproteins, such as asialoorosomucoid (ASOR). Binding of such glycoproteins or synthetic glycoconjugates to the receptor takes place with an affinity that strongly depends on the degree of branching of the oligosaccharide chain, for example, triatennary structures are bound with greater affinity than biatenarry or monoatennary chains (Baenziger and Fiete, 1980, Cell, 22, 611-620; Connolly et al., 1982, J. Biol. Chem., 257, 939-945). Lee and Lee, 1987, Glycoconjugate J., 4, 317-328, obtained this high specificity through the use of N-acetyl-D-galactosamine as the carbohydrate moiety, which has higher affinity for the receptor, compared to galactose. This “clustering effect” has also been described for the binding and uptake of mannosyl-terminating glycoproteins or glycoconjugates (Ponpipom et al., 1981, J. Med. Chem., 24, 1388-1395). The use of galactose and galactosamine based conjugates to transport exogenous compounds across cell membranes can provide a targeted delivery approach to the treatment of liver disease such as HBV and HCV infection or hepatocellular carcinoma. The use of bioconjugates can also provide a reduction in the required dose of therapeutic compounds required for treatment. Furthermore, therapeutic bioavialability, pharmacodynamics, and pharmacokinetic parameters can be modulated through the use of bioconjugates.
A number of peptide based cellular transporters have been developed by several research groups. These peptides are capable of crossing cellular membranes in vitro and in vivo with high efficiency. Examples of such fusogenic peptides include a 16-amino acid fragment of the homeodomain of ANTENNAPEDIA, a Drosophila transcription factor (Wang et al., 1995, PNAS USA., 92, 3318-3322); a 17-mer fragment representing the hydrophobic region of the signal sequence of Kaposi fibroblast growth factor with or without NLS domain (Antopolsky et al., 1999, Bioconj. Chem., 10, 598-606); a 17-mer signal peptide sequence of caiman crocodylus Ig(5) light chain (Chaloin et al., 1997, Biochem. Biophys. Res. Comm., 243, 601-608); a 17-amino acid fusion sequence of HIV envelope glycoprotein gp4114, (Morris et al., 1997, Nucleic Acids Res., 25, 2730-2736); the HIV-1 Tat49-57 fragment (Schwarze et al., 1999, Science, 285, 1569-1572); a transportan A-achimeric 27-mer consisting of N-terminal fragment of neuropeptide galanine and membrane interacting wasp venom peptide mastoporan (Lindgren et al., 2000, Bioconjugate Chem., 11, 619-626); and a 24-mer derived from influenza virus hemagglutinin envelop glycoprotein (Bongartz et al., 1994, Nucleic Acids Res., 22, 4681-4688).
These peptides were successfully used as part of an antisense oligonucleotide-peptide conjugate for cell culture transfection without lipids. In a number of cases, such conjugates demonstrated better cell culture efficacy then parent oligonucleotides transfected using lipid delivery. In addition, use of phage display techniques has identified several organ targeting and tumor targeting peptides in vivo (Ruoslahti, 1996, Ann. Rev. Cell Dev. Biol., 12, 697-715). Conjugation of tumor targeting peptides to doxorubicin has been shown to significantly improve the toxicity profile and has demonstrated enhanced efficacy of doxorubicin in the in vivo murine cancer model MDA-MB-435 breast carcinoma (Arap et al., 1998, Science, 279, 377-380).
Hudson et al., 1999, Int. J. Pharm., 182, 49-58, describes the cellular delivery of specific hammerhead ribozymes conjugated to a transferrin receptor antibody. Janjic et al., U.S. Pat. No. 6,168,778, describes specific VEGF nucleic acid ligand complexes for targeted drug delivery. Bonora et al., 1999, Nucleosides Nucleotides, 18, 1723-1725, describes the biological properties of specific antisense oligonucleotides conjugated to certain polyethylene glycols. Davis and Bishop, International PCT publication No. WO 99/17120 and Jaeschke et al., 1993, Tetrahedron Lett., 34, 301-4 describe specific methods of preparing polyethylene glycol conjugates. Tullis, International PCT Publication No. WO 88/09810; Jaschke, 1997, ACS Sympl Ser., 680, 265-283; Jaschke et al., 1994, Nucleic Acids Res., 22, 4810-17; Efimov et al., 1993, Bioorg. Khim., 19, 800-4; and Bonora et al., 1997, Bioconjugate Chem., 8, 793-797, describe specific oligonucleotide polyethylene glycol conjugates. Manoharan, International PCT Publication No. WO 00/76554, describes the preparation of specific ligand-conjugated oligodeoxyribonucleotides with certain cellular, serum, or vascular proteins. Defrancq and Lhomme, 2001, Bioorg Med Chem. Lett., 11, 931-933; Cebon et al., 2000, Aust. J. Chem., 53, 333-339; and Salo et al., 1999, Bioconjugate Chem., 10, 815-823 describe specific aminooxy peptide oligonucleotide conjugates.